The present invention relates to a printing apparatus by which a photosensitive product is provided with latent images of characters, numerals, symbols' marks or the like during the manufacture of the photographic product.
In the manufacture of photosensitve products such as photographic film, paper or the like (which is herein generically referred to as a "film"), it is usual to provide a film with latent images of characters, numerals, symbols, marks the like (which are herein generically referred to as "characters") which are later photographically developed during the processing of the exposed film, for providing information marks such as manufacturer's name, date information, film type, frame numbers, frame size and the like along the longitudinal sides or margins of the film. One way of so marking a film, which is generally called side printing, is to optically form light images of characters on the film at the longitudinal margins adjacent each picture frame during the film manufacture, the film being thereby produced with latent images of characters; and which characters are later photographically developed during the processing of the exposed film. Apparatus for producing a film with such latent images of characters as aforementioned, which are generally called side printing apparatus, are well-known as indicated by Japanese utility model No. 16589/1981, Japanese patent unexamined publication Nos. 42037/1982 and 163226/1982 and Japanese utility model unexamined publication No. 38341/1981. Such apparatus are divided into four types in accordance with their forms of light image providing arrangement. One form is a projection arrangement in which a character pattern plate and a light source for illuminating the pattern plate are used to form light images of characters, another is a light emitting diode (LED) matrix array in which a plurality of LEDs are selectively energized to form light images of characters, the third is a liquid crystal display device in combination with a light source, and the fourth is a cathode ray tube (CRT) display device.
The first arrangement aforementioned is considered to have an operational weak point in that it takes considerable time to move the character pattern plate into the required position so as to optically align the character pattern which is required to be printed with the location at which the film is printed with the latent image of the required character. Because of this, the apparatus including the first arrangement is unsuitable for high speed printing and is restricted to characters which are formed in the pattern plate. In the LED matrix array, there is the shortcoming that it is difficult to obtain a printed character of uniform density owing to the scattered luminosities and light distributions of LEDs used. Furthermore, although the CRT display device permits displaying easily any character thereon, the problems of residual images and slow response remain. A common fault observed in individual arrangements is that printing clearly a fine line is difficult. As a result, it is hard to print precisely charcters of small size or a bar code comprising heavy and fine lines in combination. Another common fault is that such arrangements are not suitable for high speed printing.